Shi Yu, Kim Hong Koo
Department of Electrical and Computer Engineering and Petersen Institute of NanoScience and Engineering, University of Pittsburgh, Pittsburgh, PA 15261, USA.
Nanophotonics. 2023 Jan 3;12(1):129-138. doi: 10.1515/nanoph-2022-0581. eCollection 2023 Jan.
We show that a circularly polarized electric dipole harbors a near-field concentrated wave which orbits around with an energy flux significantly larger (five orders of magnitudes at ∼1 nm radial distance) than far-field radiation. This near-field wave is found to carry transverse spins and reveal skyrmion spin texture (Néel-type). By performing electromagnetic analysis and numerical simulation, we demonstrate chiral extraction of a near-field rotational energy flux: the confined energy flow is out-coupled to surface plasmons on metal surface, whose curvature is designed to provide orbital angular momentum matched to spin angular momentum of dipole field, that is, to facilitate spin-orbit interaction. Strong coupling occurs with high chiral selectivity (∼113) and Purcell enhancement (∼17) when both linear and angular momenta are matched between dipole field and surface plasmons. Existence of a high-intensity energy flux in the deep-bottom near-field region ( ∼ 1 nm) opens up an interesting avenue in altering fundamental properties of dipole emission. For example, extracting ∼1% of this flux would result in enhancing spontaneous emission rate by ∼1000 times.
我们表明，圆极化电偶极子包含一个近场集中波，该波围绕其轨道运行，其能量通量比远场辐射大得多（在径向距离约为1纳米处有五个数量级）。发现这种近场波携带横向自旋并呈现出斯格明子自旋纹理（尼尔型）。通过进行电磁分析和数值模拟，我们展示了近场旋转能量通量的手性提取：受限的能量流与金属表面的表面等离子体激元外耦合，金属表面的曲率被设计为提供与偶极场的自旋角动量相匹配的轨道角动量，即促进自旋 - 轨道相互作用。当偶极场和表面等离子体激元之间的线动量和角动量都匹配时，会以高手性选择性（约113）和珀塞尔增强（约17）发生强耦合。深底部近场区域（约1纳米）中高强度能量通量的存在为改变偶极发射的基本特性开辟了一条有趣的途径。例如，提取该通量的约1%将导致自发发射率提高约1000倍。
